Synchronization scheme

ABSTRACT

In a control system for automatically synchronizing and effecting connection of a power generator to an operating power line, means are provided for sensing differences in certain frequency and phase parameters existing between the output signal of the power generator and the signal on the operating power line and thereafter generating control signals for affecting the speed of the power generator to cause any differences existing between those frequency and phase parameters to fall within defined tolerable limits. When those defined tolerable limits are achieved, means are provided for generating and transmitting a control signal to effect connection of the power generator to the operating power line.

United States Patent 1191' Konrad SYNCHRONIZATION SCHEME PrimaryExaminer-Herman Hohauser [75] Inventor: Charles Konrad Roanoke Va.Attorney, Agent, or Firm-Arnold E. Renner; Harold H. Green, Jr. [73]Assignee: General Electric Company, Salem,

Va. [57] ABSTRACT [22] Filed: Oct. 30, 1972 In a control system forautomatically synchronizing and effecting connection of a powergenerator to an [21] Appl' 302,351 operating power line, means areprovided for sensing differences in certain frequency and phaseparameters 52 us. 01. 307/87 existing between the Output signal of thePower gener- [51] int. Cl. H02j 3/08 and the signal on the operating Pand 58 Field oi Search 307/87, 57; 328/72, 133, thereafter generatingcontrol Signals for affecting the 323 134; 235 1512 speed of the powergenerator to cause any differences existing between those frequency andphase parame- 5 References Cited ters to fall within defined tolerablelimits. When those tolerable are achieved, means are pro vided forgenerating and transmitting a control signal $23? et to efiectconnection of the power generator to the op- 3,723:888 3/1973 Ellis328/134 eratmg pwer 15 Claims, 9 Drawing Figures 12 a View P POWER LINESIGNAL SOURCE i [G 2! 42 3 VAMPL Y :FREQ NEGATlVE SCOPE /-LJ r DISC 015aAND 1 OR 1 T POSlTlVE scope j 38 F SPEED l PO R GELJEERATOR I 20 l nSIGNAL SOURCE i -ANGLE SYNCHRONIZATION 4 ,DISC AND SIGNAL OR 24 i 34 23FLU? i -11? 24 FREQ O g Q DIFF K&

l% DECREASE a AND SPEED PATENTEDAPR 2 m4 SHEET 1 0F 5 SYNCHROWZATDONTRUTH TABLE SYNC PHASE ANGLE GREATER THAN :0

LESS THAN 20 SCOP E RAT E SCOPE POS NEG- LO OK PATENTEDAPR 2 m4 SHEET50F 5 owm N uwwn ww w w Q: wozmmwuhzo szmnowmu Background of theInvention The present invention relates generally to a control systemfor a power generator and more particularly to a system for effectingautomatic synchronization and safe connection of the output of a powergenerator to an operating power line of a power distribution network.

The power distribution networks which stretch across many parts of thiscountry generally include a number of satellite power generators whichare connected and disconnected periodically to augment power being fedto a main power line as the power demands increase and decreaserespectively in various parts of the networks. In view of the largepower transfers in question, however, certain parameters of the powergenerator output signal and the operating power line signal must bewithin defined, tolerable limits of each other before connection of thepower generator to the operating power line is attempted. The subjectinvention is concerned with two of these parameters, namely, phase andfrequency. Means are provided for insuring that the phase angle betweenthe power generator output signal and the operating power line signalare within a defined, safe phase angle difference from each other.Furthermore, additional means insure that the frequency of the powergenerator output signal is of a higher magnitude than the frequency ofthe operating power line signal, and also, that the difference infrequency between the two signals is within certain defined limits ofeach other; otherwise, disastrous and costly consequences would resultwhen an attempt at connection was made. For this reason, the prior arthas provided a somewhat involved scheme including at least one veryexpensive relay, as well as the need for an operator to be present toinsure alignment of the necessary signal parameters of the powergenerator output with those signal parameters on the operating powerline before a safe connection of the power generator output to theoperating power line can be made.

Summary of the Invention -If they do fall within the allowabledifferences. a synchronization signal is provided which would permitconnection of the power generator intothe operating power line. If thecompared frequency and phase parameters do not fall within the allowabledifferences, signals are provided to the power generator for causing itto change its frequency-phase relationship with that of the operatingpower line so as to meet the connection requirements.

The system disclosed in the preferred embodiment includes circuits formonitoring the frequency and phase parameters so as to insure thatconnection of the power generator to the operating power line isattempted only when the following three conditions are met: first, thephase angle existing between the frequency of the power generator outputsignal and the frequency of the operating power line signal must be lessthan 20; second, the frequency of the power generator output signal mustbe higher than the frequency of the operating power line signal; andthird, the frequency of the power generator output signal must be nomore than .33 Hz greater than the frequency of the operating power line.

The preferred embodiment further includes means responsive to each ofthe circuits monitoring the three above-mentioned parameters such thatwhen coincidence with all three circuits is achieved, a synchronizationsignal is generated and transmitted to the proper circuit effectingconnection of the power generator to the operating power line.

It is, therefore, an object of the present invention to provide a safe,economical means for automatically effecting connection of a firstalternating current source to a second alternating current source.

Another object is to provide means for comparing certain parameters ofan output signal from a first alternating current source tocorresponding parameters of a signal from a second alternating currentsource for the purpose of determining if connection of the firstalternating current source to the second alternating current source canbe safely made.

Still another object is to provide means for comparing certainparameters of an output signal from a first alternating current sourceto corresponding parameters of a second alternating source for thepurpose of determining if connection of the first alternating source tothe second alternating current source can be safely made, and ifconnection thereof cannot be safely made, means are provided for varyingthose parameters of the first alternating current source until a safeconnection can be made.

These and other objects of the subject invention will become apparentfrom the detailed description of the specification including theaccompanying drawings.

Description of the Drawings FIG. 1 is a truth table relating to theoperation of the present invention.

FIG. 2 is a basic functional block diagram of the system of the presentinvention.

FIG. 3 is a block diagram of the frequency discriminator circuitemployed in the illustrated embodiment of the present invention.

FIGS. 4(A) through 4(F) are a series of waveforms relating to theoperation of the frequency discriminator circuit of FIG. 3 under acondition of negative scope.

FIGS. 5(A) through 5(F) are'a series of waveforms relating to theoperation of the discriminator circuit of FIG. 3 under a condition ofpositive scope.

FIG. 6 is a block diagram of the angle discriminator circuit employed inthe illustrated embodiment of the present invention.

FIGS. 7(A) through 7(D) are a series of waveforms relating to theoperation of the angle discriminator circuit of FIG. 6.

FIG. 8 is a block diagram of the frequency difference circuit employedin the illustrated embodiment of the present invention.

FIGS. 9(A) through 9(F) are a series of waveforms relating to theoperation of the angle discriminator circuit of FIG. 8.

Description of the Preferred Embodiments To facilitate understanding ofthe invention, the problem to be solved should be clearly understood atthe outset/The task presented is that of connecting a first alternatingcurrent source to a second alternating current source. In a preferredembodiment of the present invention the task is more narrowly presentedas connecting a power generator, especially a gas turbine generator, toan operating power line for the purpose of augmenting the power on thepower line. It will be understood, of course, that a much broader scopeof application is contemplated. However, in referring to the preferredembodiment, in order to accomplish the task of safely connecting a powergenerator into an operating power line, certain parameters relative tothe frequency and phase of the signals from both the power generator andthe operating power line must be within defined, allowable deviationsfrom each other. The first condition that must be satisfied beforeconnection may be safely made demands that the frequency of the powergenerator output signal be higher than the generally 60 Hz frequency ofthe operating power line signal. Such a frequency relationship is termeda positive scope. When the frequency of the generator power line signalis higher than the frequency of the power generator output signal, thesituation is termed a negative scope, and under this condition,connection of the power generator to the operating power line cannot besafely madefA second condition that must be met before connection maybesafely made concerns another parameter relative to the two signals,namely that of phase angle. In order to safely connect the powergenerator into the operating power line, at the time of connection thephase angle difference between the two signals must be no greater thanAnd finally, a third condition that must be met before connection may besafely made requires that the difference in frequency between the twosignals at the time connection is attempted must be no greater than .33Hz. This difference in frequency between the two signals is generallyregarded as the scope rate and is usually expressed in terms of timerather than frequency, and a frequency difference of .33 Hz wouldcorrespond to a 3 second scope rate.

Thus, unlesszthese three conditions outlined above are met, anyattempted connection of the power generator into the operating powerline will result in an unsafe condition which, in most systems, willcause protective relays to open and thwart the attempted connection.

The invention, however, provides means for sensing the phase andfrequency parameters of the power generator and operating power line,and if the parameters are within the defined acceptable limits such thatthe three conditions are met, either an indicating means will respond tothe satisfied conditions and provide an indicating signal thereof, orelse, as shown in the preferred embodiment a synchronization signal willbe developed and transmitted toa circuit for effecting the connection ofthe power generator output to the operating power line. If the'necessary conditions are not satisfied, the system includes additionalmeans for determining whether the frequency of the power generatorshould be increased or decreased so as to bring the frequency or phaseangle within the allowable difference limits and thereby permitconnection of the power generator to the operating power line.

i As a further aid in understanding the system operation, reference isfirst made to FIG. 1 of the drawings which discloses a synchronizationtruth table of the entire system. Examination of that table, whichincludes four principle columns titled SCOPE,'SCOPE RATE, PHASE ANGLEand SYNC, indicates that safe connection of the power generator to theoperating power line is only permissible during the two conditions whichare represented by a logic one in the SYNC column. As discussed above,those two conditions exist only when there is a positive scope, whichwould be indicated in the truth table of FIG. 1 by a logic one under thefirst sub-column of the SCOPE column, entitled POS; a phase angle ofless than 20, as indicated by a logic one in the first sub-column of thephase angle column, entitled LESS THAN 20; and a scope rate of less than5 seconds as indicated by a logic one in the first or second sub-columnsof the SCOPE RATE column entitled L0 and OK respectively. The presenceof a logic one in the OK sub-column indicates that the scope rate isless than 5 seconds which is within the acceptable limits required toallow generator connection. The presence of a logic one in the LOsub-column is indicative of a SCOPE RATE of less than 3 seconds, whichis also an acceptable frequency difference to permit generatorconnection, but as will be brought out more clearly in the explanationto follow, under those conditions, when the phase angle difference isgreater than 20, the particular control signal that will be sent to thepower generator so as to cause it to increase or decrease its frequency,will depend upon whether there is a 3 or 5 second scope rate. I

Referring to FIG. 2 of the drawings, a complete system isdisclosed forcomparing a power generator output signal with an operating power linesignal for the purpose of determining if connection of the generator tothe power line is feasible. An operating power line or first alternatingcurrent signal source 12, from a power distribution network (not shown),and a power generator or second alternating current signal source 14provide sinusoidal or sine wave signals to an amplitude discriminatorcircuit 16. The amplitude discriminator circuit converts the sine wavesignals into positive going square wave signals which are then coupledfrom the amplitude discriminator circuit 16 to both frequencydiscriminator circuit 18 and an angle discriminator circuit 20.

Referring first to frequency discriminator circuit 18, a pair ofseparate output signals are taken therefrom, one of which, indicative ofa negative scope, is fed to a first AND gate 21, the other of which,indicative of a positive scope, is provided as an input to threeadditional AND gates, 22, 23 and 24. A single output is taken from anglediscriminator circuit 20 providing the only input to a frequencydifferentiator circuit 26 and a second input to AND gate 22. Frequencydifferentiator circuit 26 generates three outputs: a LO signal; and OKsignal and a HI signal. The LO signal provides a second input to ANDgate 23 and a first input to an OR gate 34, a second input to which ORgate is provided by the OK signal. OR gate 34 generates a single outputsignal in response to the presence of either the L or OK signal fromfrequency differentiator circuit 26, to provide an output signal whichserves as a third input to AND gate 22. The HI signal from frequencydifferentiator circuit 26 is introduced as the second of three inputs toAND gate 24, the third of which being an inverted output from AND gate22 An inverter circuit 38 tied to the output of AND gate 22 provides thenecessary inversion. The inverted output from inverter circuit 38 alsoprovides a second input to AND gate 21 and a third input to AND gate Theoutputs from AND gates 21 and 23 are fed to a second OR gate 42 which,when enabled, transmits a signal to the power generator for the purposeof causing the power generator to increase speed, and hence, increasefrequency. On the other hand, when AND gate 24 is enabled, a differentsignal is transmitted to the power generator for the purpose of causingthe power generator to decrease speed, and hence, decrease frequency.When the required inputs necessary to enable either OR gate 42 or ANDare not present, AND gate 22 provides an uninverted synchronizationsignal to the power generator indicating that all of the monitoredconditions necessary to allow generator connection to the operatingpower line have been met. The proper circuitry, not a part of thisinvention, will then cause the power generator to be connected into theoperating power line.

Reference is now made to FIG. 3 of the drawings which discloses a moredetailed representation of the amplitude discriminator circuit 16 andfrequency'discriminator circuit 18. Amplitude discriminator circuit 16includes a pair of squaring circuits 44 and 46, which receiverespectively the operating power line and power generator signals insine wave form from corresponding sources 12 and 14. The squaringcircuits provide square wave input signals to frequency discriminatorcircuit 18. Frequency discriminator circuit 18 receives the two inputsignals from amplitude discriminator circuit 16 through a pair ofgrounded differentiating networks, 47a and 47b, one of which, namely 47aincludes resistor 48 and capacitor 50, the other of I which, namely 47b,includes resistor 52 and capacitor 54. The differentiating networks 47aand 47b convert the square wave signals into. trigger pulses to provideinputs to the set terminals of a pair of storage cells or. bistablemultivibrators (flip flops) 56 and 58. respectively, as well as inputsto a pair of inverter circuits 60 and 6 2' respectively. An output fromeachof the inverter circuits 60. and 6 2, as well as signals from eachof the flip flops56and 58. are provided as inputs to an AND gate64which, when enabled, feeds a single output. pulse back to the clearterminals of each of the aforementioned flip flops, The purpose of usingthe outputs from the inverter circuits as additional inputs to AND gate64 is to. insure against possible race conditions which might occur inthe operation of the flip flops.

The outputsignals from flipflops 56 and58 are also provided as inputs tothe set andclear. terminals respectively. of a third storage cell orflip flop 6 6. Interposed between the outputs fromflip flops 5 6,and 58,and the inputs to the set and clear terminals of flip flop 66 are asecond pair of differentiating networks 67a.and 67b. The firstnameddifferentiating network, 67a, includes a resistor 68 and acapacitor 70 and feeds the set terminal of flip flop 66, while thesecond named differentiating network, 67a, includes a resistor 72 and acapacitor 74 and feeds the clear terminals of that flip flop. Thesenetworks are provided for converting the pulse outputs from flip flops56 and 58 into usable trigger pulses. Additional capacitors 76 and 78tied respectively between the set and clear terminals and ground, areprovided for the purpose of bypassing spike pulses generated by eitherflip flop 56 and 58 during certain periods of circuit operation.Finally, flip flop 66 provides a pair of output signals from terminals80 and 82 representing the polarity of the scope of operation. A logicone output on terminal 80 would indicate a negative scope while a logicone output on terminal 82 would represent a positive scope.

Referring now to FIGS. 4 and 5 of the drawings, each include waveforms(A) through (F) representing various signals associated with frequencydiscriminator circuit 18 under two sets of circumstances. Thosecircumstances are in one case, as in FIG. 4, when the operating powerline frequency is greater than the power generator output frequency, ora negative scope; and in the other case, as in FIG. 5, when theoperating power line frequency is less than the generator outputfrequency, or a positive scope. The waveforms (A) through (F) of bothFIGS. 4 and 5 represent the following outputs: waveform (A) representsan output signal from squaring circuit 44, while waveform (B) representsan output signal from squaring circuit 46. Waveform (C) represents anoutput signal from flip flop 56, while waveform (D) represents an outputsignal from flip flop 58. Waveforms (E) and (F) represent the signalswhich would appear on lines 80 and 82, respectively, of flip flop 66.

Reference is now made to FIG. 6 which discloses the angle discriminatorcircuit 20 in greater detail. The circuit includes a first logic meanssuch as exclusive OR gate 84 having provided thereto a pair of squarewave input signals representing the operating power line and powergenerator signals from amplitude discriminator circuit 16. The outputfrom exclusive OR gate 84 is fed to an inverter circuit 86 and an ANDgate 88. Inverter circuit 86 sends a trigger pulse to a timing meanssuch as monostable multivibrator 90 which generates a timing pulsehaving a .93 millisecond (ms) timing pulse width. The output ofmultivibrator 90 is inverted by a second inverter circuit 92, whichinverted output serves as a first input to a second logic means or ANDgate 94. The .93 ms timing pulse width of the timing pulse is arrived atby considering that at the general operating frequency of 60 Hz, thephase angle of concern whichlis 20, is equal in time to .93 ms.

A second input to AND gate 94 is taken from the output of invertercircuit 86 while an uninverted output from the monostable multivibratorserves as a second input to AND gate 88. AND gate 94 provides an inputto the set terminal of an angle discriminator storage cell, or bistablemultivibrator (flip flop) 96, the clear terminal of which has an inputsignal introduced from AND gate 88 through a resistor 98 of an RCnetwork which includes in addition to the resistor, a capacitor 1 00tiedbetween the clear terminal of flip flop 96 and groundpotential. Thepurpose of the RC network is to shape the pulse input being fed to theclear terminal of flip flop 96. An output from angle discriminatorcircuit 20 is obtained on line 101.

Referring to FIG. 7 of the drawings which includes waveforms (A) through(D), waveform (A) is representative of the lower of the operating powerline and power generator frequencies introduced into exclusive OR gate84, while waveform (B) represents the higher of the two frequencies.Waveform (C) is representative of an output signal from exclusive ORgate '84, while waveform (D) represents an output signal from flip flop96 appearing on line 101.

Referring now to FIGS. 8 and 9 of the drawings, a more detaileddisclosure of the frequency difference circuit 26 is shown in FIG. 8,while FIG. 9, reveals certain representative waveforms associated withthat circuit. the single input to frequency difference circuit 26provided from angle discriminator circuit is applied to a first triggermeans such as monostable multivibrator 102 which generates as an outputsignal, a single read pulse lasting .2 second in duration as indicatedby waveform (A) of FIG. 9. Recurring read pulses from multivibrator 102are shown as broken-line or phantom pulses a, b and c of that samewaveform. The output from multivibrator 102 is fed to a second triggermeans such as monostable multivibrator 104 which generates a longerreset pulse lasting .8 second in duration as represented by waveform (B)of FIG. 9. The output from multivibrator 104 provides an input to a pairof 2 and second time delay means 106 and 108, respectively. Time delaymeans 106, which includes output terminals 110 and 112, provides a pairof time delay signals of opposite polarity as shown representatively bywaveforms (C) and (E) respectively of FIG. 9. Time delay means 108,which includes output terminals 114 and 116, also provides a pair oftime delay signals of opposite polarity as shown representatively bywaveforms (D) and (F), respectively, of FIG. 9. Frequency differencecircuit 26 also-includes three AND gates or switch means, 118, l20'and122. AND gate 118 receives one input from multivibrator 102, and asecond input from terminal 112 of time delay means 106. AND gate 120,has provided thereto, three inputs, one from multivibrator 102, anotherfrom terminal 116 of time delay means 108 and a third from line 110 oftime delay means 106. Finally, AND gate 122 receives two inputs, onefrom terminal 114 of time delay means 108, and the other frommultivibrator 102.

AND gates 118 and 122 provide the L0 and nals respectively to OR gate 34and AND gate 24 (shown in FIG. 2) through a pair of flip flops'124 and126, while AND gate 120 provides clear signals to those flip flops aswell as the OK signals to OR gate 34.

Operation of the system will now be described by initially overviewingthe complete operation of the system and then examining each circuit inmore detail. Referring then to FIG. 2 of the drawings, it is seen thatthe signals from signal sources 12 and 14, representing signals from theoperating power line and the power generator, respectively, areintroduced as sinusoidal signals of generally different amplitudes andfrequencies into the amplitude discriminator circuit 16. The amplitudediscriminator circuit serves to convert the sinusoidal signals intopositive going square waves of equal amplitude while still preservingthe frequency and phase differences existing between the signals priorto the introduction thereto. The square waves are subsequentlytransmitted to the frequency discriminator cir-' HI sigpose of thefrequency discriminator circuit is to determine if the frequency of thegenerator output is higher (positive scope) or lower (negative scope)than the frequency on the operating power line. If a negative scope isdetected, a signal will be developed by the frequency discriminatorcircuit which, upon certain other condi- I tions being true, willincrease the speed of the power generator causing the frequency of thepower generator to increase and thereby approach a positive scope. Whena positive scope is achieved, the single to the generator causing it toincrease speed will be terminated.

Assuming then a positive scope, which is required to allow safeconnection of the power generator output to the operating power line, itis next required that the phase angle existing between the twofrequencies be less than 20 at the time connection of the powergenerator to the operating power line is made. It should be noted atthis point that since the frequencies of the two signals are generallydifferent, the phase angle existing between them at any time will varyfrom 0 to 1 over a period of time depending on the magnitude of theexisting frequency difference. The angle discriminator circuit 20 sensesthe phase angle difference between the input signals, and for thoseperiods of time during which the phase angle existing between thefrequencies is less than 20, a signal confirming that fact is generatedand transmitted to AND gate 24. Upon other conditions being met, ANDgate 24 provides a synchronization signal for causing a connection ofthe power generator to the operating power line to be made.

The frequency difference circuit 26 which receives the signal generatedby angle discriminator circuit 20 utilizes that received signal todetermine the frequency difference, or scope rate, existing between theoperating power line and the power generator output. The frequencydifference circuit 26 includes means for determining whether thefrequency difference between the operating power line and powergenerator output lies within or outside of the range of .2 Hz to .33 Hz.Expressed-in terms of time, this is equal to a 5 second scope rate and a3 second scope rate, respectively. If the frequency difference isgreater than .33 Hz (less than a 3 second scope rate) acontrol signal isgenerated and transmitted to cause the power generator to decreasespeed. If the frequency difference is less than .33 Hz (greater than a 3second scope rate), a confirming signal is transmitted through OR gate34 to a gating means such as AND gate 22 which,.assuming a positivescope and a phase angle difference of less than 20, transmits asynchronization signal to effect connection of the power generator tothe operating power line. It should be noted here, that since the phaseangle difference or the frequency difference between the operating powerline and the power generator output is meaningless unless the polarityof the scope rate ispositive, the system will not react to any signalsfrom the angle discriminator circuit 20 or the frequency differencecircuit 26 unless there is a positive scope as signaled from thefrequency discriminator circuit 18.

If the frequency difference is less than .2 Hz, the power generatoroutput may still be connected to the operating power line if the othertwo frequency parameters, namely scope polarity and phase angle, areproper and within the tolerable limits. However, assuming that there isa positive scope as required, if the phase angle below the operatingpower line and the power generator signals is greater than 20, a controlsignal will be transmitted to cause the power generator to increasespeed and thereby bring the phase angle within the required 20 phaseangle more quickly than it would have occurred at the slower speed.

A -closer examination into the operation of amplitude discriminatorcircuit 16 and the frequency discriminator 18 will now be considered.Referring to FIGS. 3, 4 and 5 of the drawings, the sine wave signalsfrom operating power line signal source 12 and power generator outputsignal source 14, are introduced respectively into the input terminalsof the squaring circuits 44 and 46 included within amplitudediscriminator 16. The squaring circuits operate on the respective inputsignals to convert them into positive going square waves of equalamplitude while still retaining frequency and phase originallyassociated therewith. The difference in frequency between the twosignals is, as stated earlier, indicative of the polarity of the scope;a higher generator output frequency being labeled a positive scope, alower generator output frequency being labeled a negative scope.

In studying the operation of the frequency discriminator circuit 18,which circuit determines the polarity of the scope, reference is made toFIG. 4 which reveals the waveforms associated wih the circuit during acondition of negative scope. Waveform (A) of that figure, being of ahigher frequency than waveform (B), would be representative of theoperating power line frequency. That signal would be fed throughsquaring circuit 44 and used to set flip flop 56. Waveform (B) of FIG.4, which is a lower frequency than that of waveform (A), isrepresentative of the power generator output frequency. That signal isfed through squaring circuit 46 of the amplitude discriminator circuit16 and used to set flip flop 58. As indicated by waveforms (C) and (D),of FIG. 4 which represent the output waveforms of flip flops 56 and 58,respectively, during a condition of negative scope flip flop 56generates a positive going square wave signal, while flip flop 58generates only positive going spike pulses. A study of the cir cuit andthe timing of the related waveforms will show that this result follows.Since flip flop 56 receives the higher frequency during a period ofnegative scope, it is set by a positive going portion of the higherfrequency, and is cleared by a clear pulse from AND gate 64 which clearpulses are generated only after receiving a positive going portion ofthe later occurring lower frequency signal. Thus, a period of timewill'elapse between the setting and clearing of flip flop 56. Thisperiod of time is the pulse width of the square wave as represented bywaveform (C) of FIG. 4. On the other hand, flip flop 58 which receives alower frequency signal during a condition of negative scope, generatesonly spike pulses out. This also follows since flip flop 58 is clearedalmost immediately after it is set because the pulse that sets that flipflop is actually the same pulse that is used to derive the pulse fromAND gate 64 used to clear that same flip flop.

With respect to positive scope, reference is made to FIG. 5. There it isseen that waveform (A) is a lower frequency than waveform (B) andrepresents the operating power line signal during a condition ofpositive scope. Waveform (B), being a higher frequency, isrepresentative of the generator output frequency during a positive scopecondition. In this instance of positive scope, the above-describedreasoning for negative any difference in scope would be completelyreversed for the flip flops 56 and 58. Flip flop 56 would generate thespike pulse while flip flop 58 would generate a square wave outputsignal.

Thus, during a condition of negative scope, flip flop 56 will generate apositive going square wave signal as represented by waveform (C) of FIG.4. Flip flop 58 will generate positive going spike pulses as representedby waveform (D) of that same figure. As a result, flip flop 66 is set bythe positive going square waves from flip flop 56. And since the spikepulses from flip flop 58 are shorted to ground through properly sizedcapacitor 78, flip flop 66 will remain set for as long as the operatingpower line frequency is greater than the power generator frequency. Flipflop 66 will generate a logic one output signal on line 80, and a logiczero output signal on line 82. These output signals are representedrespectively by waveforms (E) and (F) of FIG. 4.

During a condition of positive scope, flip flop 58 will generate apositive going square wave as represented by waveform (D) of FIG. 5.Flip flop 56 will generate positive going spike pulses as represented bywaveform (C) of that same figure. Flip flop 66 will therefore be clearedby th positive going square waves from flip flop 58 and will remaincleared as long as there exists a positive scope. This result mustfollow since the spike pulses, as represented by waveform (C) of FIG. 5,will be shorted to ground through capacitor 76, the value of whichcapacitor is is chosen so as to perform that function. Flip flop 66 willgenerate a logic zero output in response to these conditions on line 80,and a logic one output on line 82. These output signals are representedby waveforms (E) and (F), respectively, of FIG. 5.

Reference is now made to FIGS. 6 and 7 which disclose the anglediscriminator circuit 20, and waveforms relating to the operationthereof, respectively. Waveforms (A) and (B) of FIG. 7, shownarbitrarily in a condition of positive scope, represent respectively theoperating power line and power generator output signals fed fromamplitude discriminator circuit 16. The signals are introduced into theangle discriminator circuit 20 through exclusive OR gate 84, which gateresponds to the two input signals by generating a first intermediarysignal, indicated by waveform (C) of FIG. 7. The width of each pulse ofthe first intermediary signal is representative of the phase angledifference existing between the waveforms (A) and ure. The output of theangle discriminator circuit 20, shown as waveform (D) of FIG. 7, istaken from line 101 of flip flop 96, and includes a positive goingportion or phase angle signal which will persist for as long as thephase angle existing between the operating power line signal and thepower generator output signal is less than 20.

In examining the angle discriminator circuit 20 in more detail, it isseen that the positive going output pulses of the first intermediarysignal from exclusive OR gate 84 are introduced as inputs to both ANDgate 88 and inverter circuit 86. In this latter circuit, the firstintermediary signal is converted into an inverted first intermediarysignal having negative going pulses and used to feed monostablemultivibrator 90 and the AND gate 94. On the lagging or positive goingedge of the inverted first intermediary signal from inverter circuit 86,multivibrator 90 is triggered, thereby causing a timing pulse, .93 ms induration to be fed to inverter circuit 92 (B) of that same fig and toAND gate 88, the latter being enabled to generate a clear pulse wheneverboth the timing pulse and the first intermediary signal are received.The timing pulse to inverter circuit 92 is converted into an invertedtiming pulse and fed to AND gate 94, which AND gate is enabled togenerate a second intermediary signal whenever the inverted firstintermediary signal from 86 is also received therewith. And since ANDgate 94 is tied to the set terminal of flip flop 96, and AND gate 88 istied through resistor 98 to provide a third intermediary signal to theclear terminal of that same flip flop, the setting and clearing of thatflip flop provides a measure of the pulse width of waveform (C). ANDgate 94 sets flip flop 96 whenever the pulse width of waveform (C) isless than .93 ms in duration. Thus, as indicated by waveform (D) of FIG.7, a logic one output pulse or phase angle signal lasting the durationof time during which the phase angle between the two frequencies is lessthan 20, or .93 ms, is generated at the output of flip flop 96. Duringthose periods when the phase angle difference is greater than 20 a logiczero is generated.

The output from angle discriminator circuit 20, however, is useful notonly for indicating when the phase angle between the operating line andgenerator signals is iless than 20, but it is also used to determine thefrequency difference existing between those two signals. Referring toFIGS. 8 and 9 of the drawings, it is seen that the output from anglediscriminator circuit 20 is introduced into monostable multivibrator102, of the frequency difference circuit 26, which multivibratorgenerates the read pulse .2 second in duration on the leading edge orpositive going portion of the phase angle signal from the output ofangle discriminator circuit 20. This read pulse, which is representedgraphically by waveform (A) of FIG. 9, is fed to monostablemultivibrator 104 which generates the reset pulse on the lagging edge ofthe read pulse from multivibrator 102. The reset pulse lasts .8 secondin duration, and is represented by waveform (B) of FIG. 9 of thedrawings. On the lagging edge of the reset pulse, the 2 and 4 secondtime delay means, 106 and 108 respectively, are

- initiated. Thus, since the angle discriminator circuit 20 cyclicallygenerates successive output pulses which start at a precisephase anglerelationship between the two compared frequencies (namely 20), a measureof the time lapse between the successive output pulses will serve as aneffective measurement of the frequency difference existing between thetwo signals. And since multivibrator 102 is triggeredat the commencementof each pulse from the angle discriminator circuit 20 to generate a readpulse, a measure of the recurrence of those read pulses is, in-effect, ameasure of the frequency difference existing between the power generatorand operating power line.

Referring to waveforms (A) and (E) of FIG. 9 representing, respectively,the read pulse from multivibrator 102 and the signal appearing on line112, it is clear that the recurrence: of a second pulse frommultivibrator l02,'within a period of 3 seconds from a previouslycurring pulse from that multivibrator, will enable AND gate 118 whichsets flip flop 124 to generate a difference signal indicative of afrequency difference between the operating power line and the powergenerator of greater than .33 Hz. The second recurring pulse frommultivibrator 102 is indicated as phantom pulse (a) on waveform (A) ofFIG. 9 of the drawings.

Assuming 5 seconds had elapsed before the recurrence of a read pulsefrom multivibrator 102, reference is now made to waveforms (A) and (D)representing, respectively, the recurring read pulse from multivibrator102 and the signal appearing on line 114. A study of these waveformsshould make it clear that a read pulse from multivibrator 102 recurringafter 5 seconds had elapsed, as indicated by phantom pulse (c) ofwaveform (A), will enable AND gate 122 which sets flip flop 126 topermit another difference signal indicative of a frequency difference ofless than .2 Hz to be generated.

Finally, assume a recurring read pulse from multivibrator 102 isreceived after 3 seconds, but before 5 seconds has elapsed. This pulsewould be indicated by phantom pulse (b) of waveform (A). A study ofwaveforms (A), (C) and (F) will show that when a recurring read pulse isreceived at that time, AND gate will be enabled and still anotherdifference signal indicative of a frequency difference between theoperating power line and power generator voltages of less than .33 Hzbut greater than .2 Hz will be generated. The signal from AND gate 120will clear flip flops 124 and 126 if either of them had been set by asignal from either AND gate 118 or 122.

Thus, where the outputs from AND gates 118 and 122 are utilized forsetting flip flops 124 and 126 indicating, respectively, a high or lowfrequency difference between theoperating power line and the powergenerator, the output from AND gate 120, when enabled, generates asignal for clearing flip flops 124 and 126, as well as indicating thatthe difference in frequency of the two signals is acceptable. Thus, ameasure of frequency difference existing between the operating powerline. and the power generator is accomplished.

It is clear, therefore, that by the above-described invention, a controlsignal is obtained whereby the frequency of a power generator may beautomatically synchronized to the frequency of an operating power lineso as to permit safe connection of the generator voltage into the linevoltage for the purpose of augmenting the power on the operating powerline. The subject invention provides means for monitoring the scope,scope rate, and phase angle parameters of the two signals and includesfurther means for generating control signals to vary the frequency ofthe generator so as to cause that frequency to conform to certain,prescribed conditions of the monitored parameters.

While there is shown and described a specific embodiment of thisinvention, it will be understood that this invention is not limited tothe particular construction shown and described, and it is intended bythe appended claims to'cover all modifications within the spirit andscope of this invention.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. An indicating system for indicating whenever a signal from a firstalternating current source is synchronized with a signal from a secondalternating current source, said system comprising:

a. a frequency discriminator circuit responsive to the signals from saidfirst and second sources to sense a difference in frequency between saidsignals and for producing a first output signal when the frequency ofthe first source signal is higher that that of the second, and a secondoutput signal when the 13 frequency of the second source signal ishigher than that of the first;

. b. an angle discriminator circuit responsive to the signals from saidfirst and second sources to sense a phase angle difference and afrequency difference between said signals, and for generating a phaseangle signal occurring during periods of time during which said phaseangle difference is less than a predetermined value; said phase anglesignal recurring at a rate proportional to said frequency differencebetween said signals;

c. a frequency difference circuit responsive to said recurring phaseangle signals to sense a difference in frequency between said signalsfrom said first and second sources, and including first switch means forpassing a first difference signal whenever said difference in frequency,between said signals from said first and second sources is less than apreselected value; and

d. means responsive to said phase angle signal, said first output signaland said first difference signal to provide an indicating signalwhenever said phase angle signal, said first output signal and saidfirst difference signals are received.

2. The control system as recited in claim 1 wherein said phase anglesignal is a pulse having a pulse width proportional to the period oftime said phase angle difference is less than said predetermined value.

3. An indicating system for indicating whenever a signal from a firstalternating current source is synchronized with a signal from a secondalternating current source, said system comprising:

a. a frequency discriminator circuit responsive to the signals from saidfirst and second sources to sense a difference in frequency between saidsignals and for producing a first output signal when the frequency ofthe first source signal is higher than that of the second, and a secondoutput signal when the frequency of the second source signal is higherthan that of the first;

. an angle discriminator circuit responsive to the signals from saidfirst and second sources to sense a phase angle difference and afrequency difference between said signals, and for generating a, phaseangle signal occurring during periods of time during which said phaseangle difference is less than a predetermined value; said phase anglesignal recurring at a rate proportional to said frequency differencebetween said signals;

0. a frequency difference circuit responsive to said recurring phaseangle signals to sense a difference in frequency between said signalsfrom said first and second sources, said frequency, difference circuitincluding first switch means for passing a first difference signalwhenever said difference in frequency betweensaid signals from saidfirstand second sources is less than a first preselected value;

said frequency difference circuit including second switch means forpassing a second difference signal whenever said difference in,frequency between said signals from said first andsaid second sources isgreater thanasecond preselected value; said frequency difference circuitincluding third switch means for passing-third difference signal whensaid difference in frequency between saidsignals from said first andsecond sources is greater than said' nal from a first alternatingcurrent source is synchronized with a signal from a second alternatingcurrent source, said system comprising:

a. a first storage cell responsive to the signals from said first andsecond sources to provide a first signal whenever the frequency of saidsignal from said first source is greater than frequency of said signalfrom said second source;

b. a second storage cell responsive to said frequency of said signalsfrom said first and second sources to provide a second signal wheneverthe frequency of said signal from said first source is less than thefrequency of said signal from said second source;

0. a third storage cell responsive to said first and second signals toprovide a first output signal whenever said first signal is received,and a second output signal whenever said second signal is received; and

d. a frequency discriminator circuit responsive to the signals from saidfirst and second sources to sense a difference in frequency between saidsignals and .for producing a first output signal when the frequency ofthe first source signal is higher than that of the second, and a secondoutput signal when the frequency of the second source signal is higherthan that of the first.

5. A control system for synchronizing a signal from a first alternatingcurrent source to a signal from a second alternating current source,said system comprising:

a. a frequency discriminator circuit responsive to the signals from saidfirst and second sources to sense a difference in frequency between saidsignals and for producing-a first output signal when the frequency ofthe first source signal is higher than that of the second, and a secondoutput signal when the frequency of the second source signal is higherthan that of the first;

. an angle discriminator circuit responsive to the signals from saidfirst and second sources to sense a phase angle difference and afrequency difference between said signals, and for generating a phaseangle signal occurring during periods of time during which said phaseangle difference is less than a predetermined value; said phase anglesignal recurring at a rate proportional to said frequency differencebetween said signals;

c. a frequency difference circuit responsive to said recurring phaseangle signals to sense a difference in frequency between the signalsfrom said first and second sources, and including first switch means forpassing a first difference signal whenever said difference in frequencybetween said signals from said first and second sources is less than apreselected value; and

d. a first gating means responsive to said phase angle signal, saidfirst output signal and said first difference signal to provide asynchronization signal for effecting connection of said first source tosaid second'source.

6. A control system for synchronizing a signal from a first alternatingcurrent source to a signal from a second alternating current source,said system comprising:

a; a frequency discriminator circuit responsive to the signals from saidfirst and second sources to sense a difference in frequency between saidsignals and for producing a first output signal when the frequency ofthe first source signal is higher than that of the second, and a secondoutput signal when the frequency of the second source signal is higherthan that of the first; an angle discriminator circuit responsive tothe'siga frequency difference circuit responsive to said recurring phaseangle signals to sense a difference in frequency between said signalsfrom said first and second sources, and including first switch means forpassing a first difference signal whenever said difference in frequencybetween said signals from said first and second sources is less than afirst preselected value; second switch means for passing a seconddifference signal when said difference in frequency between said signalsfrom said first and i said second sources is greater than a secondpreselected value; third switch means for passing a third differencesignal said difference in frequency between said signals from said firstand second sources is greater than said first preselected value and lessthan said second preselected value; and

d. a first gating means responsive to said phase angle signal, saidfirst output signal and said first or said third difference signal toprovide a synchronization signal for effecting connection of said firstsource to said second source.

in frequency between said signals from said first and second sources,and including first switch means for passing a first difference signalwhenever said difference in frequency between said signals from saidfirst and second sources is less than a first preselected value; secondswitch means for passing a second difference signal whenever saiddifference in frequency between said signals from said first and saidsecond sources is greater than a second preselected value; third switchmeans for producing a third difference signal when said difference infrequency between said signals from said first and second sources isgreater than said first preselected value and less than said secondpreselected value;

e. a second gating means responsive to said second output signal andsaid nonsynchronization signal to initiate a first intermediary controlsignal;

f. a third gating means responsive to said second difference signal,said first output signal and said nonsynchronization signal to initiatea first control signal for causing said frequency of said signal fromsaid first source to increase in a first direction;

g. a fourth gating means responsive to said first output signal, saidfirst difference signal and said nonsynchronization signal to initiate asecond intermediary control signal; and

h. a fifth gating means responsive to said first and second intermediarycontrol signals to initiate a second control signal for causing saidfrequency of said signal from said first source to increase in a seconddirection opposite to said first direction.

8. The control system as recited in claim 7 wherein 7. A control systemfor synchronizing a signal from a first alternating current source to asignal from a second alternating current source, said system comprising:

said first alternating current source is a power generator and saidsecond alternating current source is an operating power line.

9. The control system as recited in claim 8 wherein a. a frequencydiscriminator circuit responsive to the said power generator is a gasturbine generator.

signals from said first and second sources to sense a difference infrequency between said signals and for producing a first output signalwhen the frequency of the first source signal is higher than that of thesecond, and a second output signal when the frequency of the secondsource signal is higher than that of the first;

. an angle discriminatorcircuit responsive to the signals from saidfirst and second sources to sense a phase angle difference anda'frequency difference.

. a frequency difference circuit responsive to said recurring phaseangle signals to sense a difference 5O 10. The control system as recitedin claim 7 wherein said signal from said first source [S less than thefrequency of said signal from said second source; and

c. a third storage cell responsive to said first and second signals toprovide a first output signal whenever said first signal is received,and a second output signal whenever said second signal is received.

11. The control system as recited in claim 7 wherein said anglediscriminator circuit comprises:

a. a first logic means responsive to said frequency of termediary signalto generate a timing pulse having a pulse width representative of saidpredetermined value;

d. a second inverter circuit, said second inverter circuit responsive tosaid timing pulse to generate an inverted timing pulse;

e. second logic means responsive to said inverted timing pulse and saidinverted first intermediary signal to produce a second intermediarysignal whenever said pulse width of said inverted timing pulse isgreater than said pulse width of said inverted first intermediarysignal;

third logic means responsive to said first intermediary signal and saidtiming pulse to generate a third intermediary signal whenever said pulsewidth of said first intermediary signal is greater than said pulse widthof said timing pulse; and

g. an angle discriminator storage cell, responsive to said second andsaid third intermediary signals to generate said phase angle signalwhenever said pulse width of said first intermediary signal is less thansaid pulse width of said timing pulse.

12. The control system as recited in claim 7 wherein said frequencydifference circuit comprises:

a. first trigger means responsive to said phase angle signal to generatea read pulse;

b. second trigger means responsive to said read pulse to generate areset pulse;

c. a first time delay means responsive to said reset pulse to producefirst and second time delay signals;

d. a second time delay means responsive to said reset pulse to producethird and fourth time delay signals;-

e. said first switch means responsive to said read pulse and said firsttime delay signal to produce said first difference signals whenever saiddifference in frequency between said signals from said first and saidsecond sources is less than said first preselected value;

. said second switch means responsive to said read pulse and said thirdtime delay signal to produce said second difference signal whenever saiddiffer- 18 ence in frequency between said signals from said first andsecond sources is greater than said second preselected value; and

g. said third switch means responsive to said read pulse, said secondtime delay signal and said fourth time delay signal to produce saidthird difference signal whenever said difference in frequency betweensaid first and said second sources is greater than said firstpreselected value and less than said second preselected value.

13. The control system as recited in claim 12 wherein said first timedelay signal has a polarity opposite that of said second time delaysignal, and said third time delay signal has a polarity opposite that ofsaid fourth time delay signal.

14. A frequency difference circuit for sensing a difference in frequencybetween signals from first and second alternating current sources, saidcircuit comprising:

a. first trigger means responsive to a phase angle signal to generate aread pulse;

b. second trigger means responsive to said read pulse to generate areset pulse;

0. a first time delay means responsive to said reset pulse to producefirst and second time delay sig nals;

d. a second time delay means responsive to said reset pulse to producethird and fourth time delay signals;

e. a first switch means responsive to said read pulse and said firsttime delay signal to produce a first difference signal whenever saidsignals from said first and second sources is less than a firstpreselected value;

f. a second switch means responsive to said read pulse and said thirdtime delay signal to produce a second difference signal whenever saiddifference in frequency between said signals from said first and secondsources is greater than a second preselected value; and

g. a third switch means responsive to said read pulse, said second timedelay signal and said fourth time delay signal to produce a thirddifference signal whenever said difference in frequency between saidfirst and second sources is greater than said first preselected valueand less than said second preselected value.

15. The control system as recited in claim 14 wherein said first timedelay signal has a polarity opposite that of said second time delaysignal, and said third time delay of signal has polarity opposite thatof said fourth time delay signal.

1. An indicating system for indicating whenever a signal from a firstalternating current source is synchronized with a signal from a secondalternating current source, said system comprising: a. a frequencydiscriminator circuit responsive to the signals from said first andsecond sources to sense a difference in frequency between said signalsand for producing a first output signal when the frequency of the firstsource signal is higher that that of the second, and a second outputsignal when the frequency of the second source signal is higher thanthat of the first; b. an angle discriminator circuit responsive to thesignals from said first and second sources to sense a phase angledifference and a frequency difference between said signals, and forgenerating a phase angle signal occurring during periods of time duringwhich said phase angle difference is less than a predetermined value;said phase angle signal recurring at a rate proportional to saidfrequency difference between said signals; c. a frequency differencecircuit responsive to said recurring phase angle signals to sense adifference in frequency between said signals frOm said first and secondsources, and including first switch means for passing a first differencesignal whenever said difference in frequency between said signals fromsaid first and second sources is less than a preselected value; and d.means responsive to said phase angle signal, said first output signaland said first difference signal to provide an indicating signalwhenever said phase angle signal, said first output signal and saidfirst difference signals are received.
 2. The control system as recitedin claim 1 wherein said phase angle signal is a pulse having a pulsewidth proportional to the period of time said phase angle difference isless than said predetermined value.
 3. An indicating system forindicating whenever a signal from a first alternating current source issynchronized with a signal from a second alternating current source,said system comprising: a. a frequency discriminator circuit responsiveto the signals from said first and second sources to sense a differencein frequency between said signals and for producing a first outputsignal when the frequency of the first source signal is higher than thatof the second, and a second output signal when the frequency of thesecond source signal is higher than that of the first; b. an anglediscriminator circuit responsive to the signals from said first andsecond sources to sense a phase angle difference and a frequencydifference between said signals, and for generating a phase angle signaloccurring during periods of time during which said phase angledifference is less than a predetermined value; said phase angle signalrecurring at a rate proportional to said frequency difference betweensaid signals; c. a frequency difference circuit responsive to saidrecurring phase angle signals to sense a difference in frequency betweensaid signals from said first and second sources, said frequencydifference circuit including first switch means for passing a firstdifference signal whenever said difference in frequency between saidsignals from said first and second sources is less than a firstpreselected value; said frequency difference circuit including secondswitch means for passing a second difference signal whenever saiddifference in frequency between said signals from said first and saidsecond sources is greater than a second preselected value; saidfrequency difference circuit including third switch means for passingthird difference signal when said difference in frequency between saidsignals from said first and second sources is greater than said firstpreselected value and less than said second preselected value; and d.means responsive to said phase angle signal, said first output signaland said first or second difference signals to provide an indicatingsignal whenever said phase angle signal, said first output signal andsaid first or second difference signals are received.
 4. An indicatingsystem for indicating whenever a signal from a first alternating currentsource is synchronized with a signal from a second alternating currentsource, said system comprising: a. a first storage cell responsive tothe signals from said first and second sources to provide a first signalwhenever the frequency of said signal from said first source is greaterthan frequency of said signal from said second source; b. a secondstorage cell responsive to said frequency of said signals from saidfirst and second sources to provide a second signal whenever thefrequency of said signal from said first source is less than thefrequency of said signal from said second source; c. a third storagecell responsive to said first and second signals to provide a firstoutput signal whenever said first signal is received, and a secondoutput signal whenever said second signal is received; and d. afrequency discriminator circuit responsive to the signals from saidfirst and second sources to sense a difference in frequency between saidsignals and for producIng a first output signal when the frequency ofthe first source signal is higher than that of the second, and a secondoutput signal when the frequency of the second source signal is higherthan that of the first.
 5. A control system for synchronizing a signalfrom a first alternating current source to a signal from a secondalternating current source, said system comprising: a. a frequencydiscriminator circuit responsive to the signals from said first andsecond sources to sense a difference in frequency between said signalsand for producing a first output signal when the frequency of the firstsource signal is higher than that of the second, and a second outputsignal when the frequency of the second source signal is higher thanthat of the first; b. an angle discriminator circuit responsive to thesignals from said first and second sources to sense a phase angledifference and a frequency difference between said signals, and forgenerating a phase angle signal occurring during periods of time duringwhich said phase angle difference is less than a predetermined value;said phase angle signal recurring at a rate proportional to saidfrequency difference between said signals; c. a frequency differencecircuit responsive to said recurring phase angle signals to sense adifference in frequency between the signals from said first and secondsources, and including first switch means for passing a first differencesignal whenever said difference in frequency between said signals fromsaid first and second sources is less than a preselected value; and d. afirst gating means responsive to said phase angle signal, said firstoutput signal and said first difference signal to provide asynchronization signal for effecting connection of said first source tosaid second source.
 6. A control system for synchronizing a signal froma first alternating current source to a signal from a second alternatingcurrent source, said system comprising: a. a frequency discriminatorcircuit responsive to the signals from said first and second sources tosense a difference in frequency between said signals and for producing afirst output signal when the frequency of the first source signal ishigher than that of the second, and a second output signal when thefrequency of the second source signal is higher than that of the first;b. an angle discriminator circuit responsive to the signals from saidfirst and second sources to sense a phase angle difference and afrequency difference between said signals, and for generating a phaseangle signal occurring during periods of time during which said phaseangle difference is less than a predetermined value; said phase anglesignal recurring at a rate proportional to said frequency differencebetween said signals; c. a frequency difference circuit responsive tosaid recurring phase angle signals to sense a difference in frequencybetween said signals from said first and second sources, and includingfirst switch means for passing a first difference signal whenever saiddifference in frequency between said signals from said first and secondsources is less than a first preselected value; second switch means forpassing a second difference signal when said difference in frequencybetween said signals from said first and said second sources is greaterthan a second preselected value; third switch means for passing a thirddifference signal said difference in frequency between said signals fromsaid first and second sources is greater than said first preselectedvalue and less than said second preselected value; and d. a first gatingmeans responsive to said phase angle signal, said first output signaland said first or said third difference signal to provide asynchronization signal for effecting connection of said first source tosaid second source.
 7. A control system for synchronizing a signal froma first alternating current source to a signal from a second alternatingcurrent source, said system Comprising: a. a frequency discriminatorcircuit responsive to the signals from said first and second sources tosense a difference in frequency between said signals and for producing afirst output signal when the frequency of the first source signal ishigher than that of the second, and a second output signal when thefrequency of the second source signal is higher than that of the first;b. an angle discriminator circuit responsive to the signals from saidfirst and second sources to sense a phase angle difference and afrequency difference between said signals, and for generating a phaseangle signal occurring during periods of time during which said phaseangle difference is less than a predetermined value; said phase anglesignal recurring at a rate proportional to said frequency differencebetween said signals; c. a frequency difference circuit responsive tosaid recurring phase angle signals to sense a difference in frequencybetween said signals from said first and second sources, and includingfirst switch means for passing a first difference signal whenever saiddifference in frequency between said signals from said first and secondsources is less than a first preselected value; second switch means forpassing a second difference signal whenever said difference in frequencybetween said signals from said first and said second sources is greaterthan a second preselected value; third switch means for producing athird difference signal when said difference in frequency between saidsignals from said first and second sources is greater than said firstpreselected value and less than said second preselected value; d. afirst gating means having first and second states and being responsiveto said phase angle signal, said first output signal and said first orsaid third difference signal to assume said first state and provide asynchronization signal for effecting connection of said first source tosaid second source, said first gating means assuming said second stateto provide a nonsynchronization signal whenever said phase angle signal,said first output signal and said first or said third difference signalsare not present; e. a second gating means responsive to said secondoutput signal and said nonsynchronization signal to initiate a firstintermediary control signal; f. a third gating means responsive to saidsecond difference signal, said first output signal and saidnonsynchronization signal to initiate a first control signal for causingsaid frequency of said signal from said first source to increase in afirst direction; g. a fourth gating means responsive to said firstoutput signal, said first difference signal and said nonsynchronizationsignal to initiate a second intermediary control signal; and h. a fifthgating means responsive to said first and second intermediary controlsignals to initiate a second control signal for causing said frequencyof said signal from said first source to increase in a second directionopposite to said first direction.
 8. The control system as recited inclaim 7 wherein said first alternating current source is a powergenerator and said second alternating current source is an operatingpower line.
 9. The control system as recited in claim 8 wherein saidpower generator is a gas turbine generator.
 10. The control system asrecited in claim 7 wherein said frequency discriminator circuitcomprises: a. a first storage cell responsive to the signals from saidfirst and second sources to provide a first signal whenever thefrequency of said signal from said first source is greater than thefrequency of said signal from said second source; b. a second storagecell responsive to said frequency of said signals from said first andsecond sources to provide a second signal whenever the frequency of saidsignal from said first source is less than the frequency of said signalfrom said second source; and c. a third storage cell responsive to saidfirst and second signals to provide a first output signal whenever saidfirst signal is received, and a second output signal whenever saidsecond signal is received.
 11. The control system as recited in claim 7wherein said angle discriminator circuit comprises: a. a first logicmeans responsive to said frequency of said signals from said first andsecond sources to produce a first intermediary signal having a pulsewidth representative of said phase angle difference between saidfrequencies; b. a first inverter circuit responsive to said firstintermediary signal to generate an inverted first intermediary signal;c. a timing means responsive to said inverted first intermediary signalto generate a timing pulse having a pulse width representative of saidpredetermined value; d. a second inverter circuit, said second invertercircuit responsive to said timing pulse to generate an inverted timingpulse; e. second logic means responsive to said inverted timing pulseand said inverted first intermediary signal to produce a secondintermediary signal whenever said pulse width of said inverted timingpulse is greater than said pulse width of said inverted firstintermediary signal; f. third logic means responsive to said firstintermediary signal and said timing pulse to generate a thirdintermediary signal whenever said pulse width of said first intermediarysignal is greater than said pulse width of said timing pulse; and g. anangle discriminator storage cell, responsive to said second and saidthird intermediary signals to generate said phase angle signal wheneversaid pulse width of said first intermediary signal is less than saidpulse width of said timing pulse.
 12. The control system as recited inclaim 7 wherein said frequency difference circuit comprises: a. firsttrigger means responsive to said phase angle signal to generate a readpulse; b. second trigger means responsive to said read pulse to generatea reset pulse; c. a first time delay means responsive to said resetpulse to produce first and second time delay signals; d. a second timedelay means responsive to said reset pulse to produce third and fourthtime delay signals; e. said first switch means responsive to said readpulse and said first time delay signal to produce said first differencesignals whenever said difference in frequency between said signals fromsaid first and said second sources is less than said first preselectedvalue; f. said second switch means responsive to said read pulse andsaid third time delay signal to produce said second difference signalwhenever said difference in frequency between said signals from saidfirst and second sources is greater than said second preselected value;and g. said third switch means responsive to said read pulse, saidsecond time delay signal and said fourth time delay signal to producesaid third difference signal whenever said difference in frequencybetween said first and said second sources is greater than said firstpreselected value and less than said second preselected value.
 13. Thecontrol system as recited in claim 12 wherein said first time delaysignal has a polarity opposite that of said second time delay signal,and said third time delay signal has a polarity opposite that of saidfourth time delay signal.
 14. A frequency difference circuit for sensinga difference in frequency between signals from first and secondalternating current sources, said circuit comprising: a. first triggermeans responsive to a phase angle signal to generate a read pulse; b.second trigger means responsive to said read pulse to generate a resetpulse; c. a first time delay means responsive to said reset pulse toproduce first and second time delay signals; d. a second time delaymeans responsive to said reset pulse to produce third and fourth timedelay signals; e. a first switch means responsive to said read pulse andsaid first time delay signal to produce a first difference signalwhenever said signals from said first and second sources is less than afirst preselected value; f. a second switch means responsive to saidread pulse and said third time delay signal to produce a seconddifference signal whenever said difference in frequency between saidsignals from said first and second sources is greater than a secondpreselected value; and g. a third switch means responsive to said readpulse, said second time delay signal and said fourth time delay signalto produce a third difference signal whenever said difference infrequency between said first and second sources is greater than saidfirst preselected value and less than said second preselected value. 15.The control system as recited in claim 14 wherein said first time delaysignal has a polarity opposite that of said second time delay signal,and said third time delay of signal has polarity opposite that of saidfourth time delay signal.